The present invention relates to an improved method for plasma etching anti-reflective coatings in the fabrication of integrated circuits.
A common requirement in integrated circuit fabrication is the etching of openings such as contacts, vias and trenches in dielectric materials. The dielectric materials include doped silicon oxide such as fluorinated silicon oxide (FSG), undoped silicon oxide such as silicon dioxide, silicate glasses such as boron phosphate silicate glass (BPSG) and phosphate silicate glass (PSG), doped or undoped thermally grown silicon oxide, doped or undoped TEOS deposited silicon oxide, etc. The dielectric dopants include boron, phosphorus and/or arsenic. The dielectric can overlie a conductive or semiconductive layer such as polycrystalline silicon, metals such as aluminum, copper, titanium, tungsten, molybdenum or alloys thereof, nitrides such as titanium nitride, metal suicides such as titanium silicide, cobalt silicide, tungsten silicide, molybdenum silicide, etc.
Various plasma etching techniques for etching openings in silicon oxide are disclosed in U.S. Pat. Nos. 5,013,398; 5,013,400; 5,021,121; 5,022,958; 5,269,879; 5,529,657; 5,595,627; 5,611,888; and 5,780,338. The plasma etching can be carried out in medium density reactors such as the parallel plate plasma reactor chambers described in the ""398 patent or the triode type reactors described in the ""400 patent or in high density reactors such as the inductive coupled reactors described in the ""657 patent. U.S. Pat. No. 6,090,304 discloses a method of plasma etching semiconductor substrates in a dual frequency plasma reactor wherein a first radiofrequency (RF) source is coupled to a top showerhead electrode through an RF matching network and a bottom electrode (on which a semiconductor wafer is supported) is coupled to a second RF source through a second matching network.
In processing semiconductor wafers, it is conventional to provide an organic bottom antireflective coating (ARC) beneath a photoresist for purposes of minimizing optical reflection of the radiation used to develop a pattern of openings (such as contact holes) in the photoresist. It is also conventional to plasma etch the ARC through the openings formed in the resist in order to transfer the photoresist pattern to the ARC. Etch gas mixtures for plasma etching organic ARC materials are disclosed in U.S. Pat. Nos. 5,721,090; 5,773,199; 5,910,453; 6,039,888; 6,080,678; and 6,090,722. Of these, the ""090 patent discloses a gas mixture of C4F8, O2 and N2, the ""199 patent discloses a gas mixture of CHF3+CF4+O2+Ar; the ""453 patent discloses gas mixtures of N2+He+O2 or N2+O2 or N2+He; the ""888 patent discloses a gas mixture of O2+CO; the ""678 patent discloses a gas mixture of O2+SO2; and the ""722 patent discloses a gas mixture of C2F6+Ar.
As device geometries become smaller and smaller, the need for high etch selectivity ratios is even greater in order to achieve plasma etching openings through ARC layers while preserving critical dimensions (CD). Selectivity is also desirable when etching organic ARC layers having areas of different thicknesses since the underlying material will be exposed to the etching gas for longer times in the areas which underlie the thinner portions of the ARC. Accordingly, there is a need in the art for a plasma etching technique which provides high etch selectivity ratios and/or which etches such layers at a desirable rate.
The invention provides a method of etching an organic anti-reflective coating (ARC) with selectivity to an overlying photoresist and/or underlying dielectric layer, comprising supporting a semiconductor substrate in a plasma etch reactor, the substrate including an organic anti-reflective coating (ARC) between an underlying dielectric layer and an overlying photoresist layer, and energizing a fluorine-free etchant gas into a plasma state and etching openings in the ARC, the etchant gas comprising a carbon-containing gas and a nitrogen-containing gas. In a preferred embodiment, the etching gas further includes O2 and/or an inert gas such as Ar.
According to a preferred embodiment, the openings comprise vias, contacts, and/or trenches of a dual damascene or self-aligned structure and/or the ARC is a polymer film. The plasma etch reactor can comprise an ECR plasma reactor, an inductively coupled plasma reactor, a capacitively coupled plasma reactor, a helicon plasma reactor or a magnetron plasma reactor. A preferred plasma etch reactor is a dual frequency capacitively coupled plasma reactor including an upper showerhead electrode and a bottom electrode, RF energy being supplied at two different frequencies to either the bottom electrode or at different first and second frequencies to the showerhead electrode and the bottom electrode.
During the etching step, pressure in the plasma etch reactor can be up to 200 mTorr and/or temperature of the substrate support can be xe2x88x9220xc2x0 C. to +200xc2x0 C., preferably +20xc2x0 C. to +50xc2x0 C. The etching gas can include CO as the carbon-containing gas supplied to the plasma etch reactor at a flow rate of 1 to 500 sccm, O2 supplied to the plasma etch reactor at a flow rate of 1 to 50 sccm, and the nitrogen-containing gas can include N2 supplied to the plasma etch reactor at a flow rate of 0 to 250 sccm. The etch gas can optionally include Ar as the inert gas supplied to the plasma etch reactor at a flow rate of 0 to 500 sccm. As an example, the etching gas can include 50 to 500 sccm CO, 2 to 10 sccm O2, 50 to 150 sccm N2, and 100 to 300 sccm Ar.
The etching step can be followed by additional etching steps and subsequent filling of the openings with metal. The method of the invention can also include steps of forming the photoresist layer on the substrate, patterning the photoresist layer to form a plurality of openings followed by etching a metallization pattern of conductor lines, via or contact openings in the organic anti-reflective coating.